The present invention relates generally to the field of detecting the onset of ovulation in the human female based upon the evaluation of peripheral changes preceding, coinciding with, and succeeding the ovulatory process. More specifically, it relates to a method and associated apparatus for estimating the period of peak fertility in the human menstrual cycle for the purposes of natural contraceptive practice and fertility enhancement, by observing cyclic changes in daily quantities of cervico-vaginal fluid which accumulates naturally in the vagina.
Because of cultural or religious beliefs in certain populations and increased dissatisfaction with adverse side effects and inconvenience of hormonal, chemical or mechanical and other contraceptive methods, there is considerable present interest in a simple, practical, convenient, reliable, and effective method of birth control using natural, non-invasive techniques. Additionally, the ability to accurately detect the time of ovulation is critical where conception is desired, since after ovulation the ovum remains viable for fertilization for approximately 12-24 hours. A simple method for determining the onset of ovulation, therefore, is desirable also for fertility enhancement.
Over the past two decades there has been much research to develop techniques of ovulation timing and associated apparatus for birth control and fertility enhancement purposes. The occurrence of ovulation can be detected with some accuracy through various state of the art methods. At present these methods can give a reasonably good indication that ovulation has occurred or is imminent. However, each of these methods is subject to certain disadvantages which effect either its practicality or its reliability as a method which can be conveniently used and accurately interpreted by female subjects without medical aid and/or highly sophisticated laboratory methods.
One clinical technique suggested as a method of detecting the time of ovulation relies on a woman's ability to detect some degree of pelvic discomfort at mid-cycle, the time of expected ovulation. Distention of the ovary or peritoneal irritation as a result of follicular rupture are the probable causes of this "mittelschmerz." Unfortunately, because most patients do not experience or cannot reliably identify monthly "mittelschmerz," it is not a widely applicable or reliable method to detect ovulation.
For years the physical properties of cervical mucus have been used by clinicians to roughly establish the fertile period. Recently Hilgers, et al. Ob/Gyn, 52, 575-582, (1978) have confirmed that ovulation occurs from 3 days before to 3 days after the last day of cervical mucus symptoms (copious mucus flow, ferning, spinnbarkeit, and minimum viscoelasticity). Cervical mucus is a hydrogel secreted in the cervical portion of the uterus which, for purposes of clinical examination, must be removed from the mouth of the cervix with specially designed instruments by medical personnel. A woman cannot obtain cervical mucus by self-use of such methods or devices. See U.S. Pat. Nos. 3,926,037; 4,002,056; 4,013,066; 3,979,945.
Self-observation of the color or viscoelasticity of a mucoid vaginal discharge (cervical mucus plus vaginal discharges) to detect ovulation has also been advocated as a method of birth control. Wilson, M.A., The Ovulation Method of Birth Regulation, Van Nostrand Reinhold Co., N.Y. 1980. In its present form this method of birth control, called the "Ovulation" or "Billings" Method, is entirely qualitative and subjective, depending upon a woman's ability to perceive the characteristic appearance of a midcycle mucoid discharge at the opening of the vagina. The method is complicated by the fact that some women are scant cervical mucus and vaginal fluid producers, even at ovulation, making identification of mucus symptoms difficult. Some studies using this method of fertility regulation for birth control purposes have shown a failure rate of approximately 25%. [Moghissi, K. S., Fertil. Steril., 34, 89, (1980); World Health Organization, "A Prospective Multicentre Trial of the Ovulation Method of Natural Family Planning. II. The Effectiveness Phase," Fertil. Steril., 36, 591, (1981).]
Perhaps the presently most popular and widely used method of detecting ovulation is the graphic recording of the waking temperature at basal conditions. A significant rise in Basal Body Temperature (BBT) normally occurs 1-2 days after ovulation. Three consecutive BBT readings should be at least 0.2.degree. C. (approximately 0.36.degree. F) higher than the previous six daily temperatures in order to establish the infertile period. (Moghissi, K. S., Fertil.Steril., 34, 89, 1980). There are several drawbacks to this method. Only basal conditions can be used; that is, a female subject must get 6-8 hours of sleep and must take her temperature immediately on awakening. Physical activity and/or alcohol consumption the night before or intermittent infections can result in spurious temperatures. A very important consideration is that BBT measurements do not indicate when ovulation is approaching, but rather provide evidence of ovulation 2 or 3 days after it has occurred. Additionally, many times a BBT chart can be difficult for a woman to interpret accurately.
Many other attempts to detect ovulation involve biochemical and histological evaluations of epithelial or endometrial samples, and the monitoring of hormone levels in the blood, all of which require medical expertise and sophisticated equipment and therefore are unsuited for self-use.
Several attempts to discover a simple method for self-detection of the fertile, ovulatory phase are reflected in U.S. patents. Preti, et al., U.S. Pat. No. 4,119,089 suggests a method of predicting and determining the time of ovulation by monitoring the concentration of volatile sulfur-containing compounds present in mouth air, using gas chromatography, a technique not practical for home use.
A more recent technique developed for self-use is described in Polishuk U.S. Pat. No. 4,151,833. This method teaches the detection of ovulation by measuring the water content in the vaginal cavity, using a pellet made of a hydrophilic polymer. Practice of this method involves insertion of the pellet into the vagina for approximately 8 hours every day and measurement of the pellet diameter to detect an increase in water content of cervical mucus, allegedly indicative of onset of ovulation. This method has practical disadvantages for the woman involved, including discomfort and interference with sexual activity while the pellet is in place. More importantly, the method also suffers from several interpretive disadvantages.
Cervical mucus is a hydrogel from which it is difficult to extract water. Additionally, the contents of the vagina include particulate matter, i.e., epithelial cells, bacteria, gelatinous glycoprotein strands (from cervical mucus), etc., as well as water containing serum transudate. Since much human tissue, including vaginal tissue, is 90% water, there is no way of determining what water content the pellet method is measuring during prolonged exposure of the hydrophilic pellet material to the vaginal environment. The swelling of the pellet represents the uptake of water over a long period of time during which the pellet may itself be interfering with the water equilibrium of the vaginal tissue. Any changes in water correlated with the menstrual cycle would tend to be obscured by the large total volume of water necessarily absorbed over approximately 8 hours. Furthermore, the probability of inaccuracy is great because the swelling of the pellet can only be measured by an increase in diameter; in addition, the swelling is a function of the absorbent capacity of the polymer. All of these disadvantages demonstrate the inadequacy of this method in providing a reliable and accurate means of self-detection of ovulation.
Despite the wealth of prior techniques described for ovulation detection, therefore, there remains a need for a method which is simple and reliable in both application and interpretation for self-detection of the fertile period of the human menstrual cycle.